Optimizing application of entomopathogenic nematodes to manage large pine weevil, Hylobius abietis L. (Coleoptera:Curculionidae) populations developing in pine stumps, Pinus sylvestris

Abstract

Hylobius abietis develops in stumps of recently felled coniferous trees, and adults emerge to feed on and kill young seedlings. Entomopathogenic nematodes applied to stumps containing late instar larvae and pupae can reduce the number of adults emerging. We tested the feasibility of reduced application rate and volume during a broader window of application in Weld trials in 2004 and 2005. Application at the standard rate of 3.5 million infective juveniles per stump suppressed the number of adults emerging by up to 79-85% relative to controls for Heterorhabditis downesi, 57-64% for Steinernema carpocapsae and 51-56% for S. feltiae. When the application rate was halved, only H. downesi gave a signiWcant reduction in emergence (75-79%). Nematodes applied in April, May or June signiWcantly reduced weevil populations, and application of nematode-killed insects in May was as eVective as an aqueous suspension. A fourfold reduction in application volume from 500 to 125 ml per stump did not aVect the percentage of weevils parasitized, and stump excavation revealed that even at the reduced volume, both S. carpocapsae (ambusher) and H. downesi (cruiser) parasitized weevils 40-49 cm from the bole and 40-49 cm below soil level. A higher percentage of larvae (60%) were infected than either pupae (36%) or callow adults (18%). Our trials show promise for expanding the use of entomopathogenic nematodes against pine weevil, as the standard application rate can be halved, and the volume reduced to 25% of the standard without signiWcant loss of eYcacy, and there is a wide window of opportunity for application, even when soil temperatures are as low as 9°C.

The lethal and sub-lethal consequences of entomopathogenic nematode infestation and exposure for adult pine weevils, Hylobius abietis (Coleoptera: Curculionidae)

“…04.003 in forestry in the UK and Ireland against which pesticide is routinely applied (Willoughby et al, 2004). As a possible alternative, entomopathogenic nematodes (EPN) have been trialed for the biological control of H. abietis (Pye and Pye, 1985;Brixey, 2000;Brixey et al, 2006;Dillon et al, 2006Dillon et al, , 2007Torr et al, 2007). EPN in the families Steinernematidae and Heterorhabditidae are lethal parasites of a broad variety of insect species (Poinar, 1979).…”

Optimizing the application method of entomopathogenic nematode suspension for biological control of large pine weevil Hylobius abietis

“…Biological control of the large pine weevil Hylobius abietis (Coleoptera: Curculionidae) (LPW) using entomopathogenic nematodes (EPNs) has become a feasible sustainable method over the last decade (Torr et al 2005;Brixey et al 2006;Dillon et al 2006Dillon et al , 2007Dillon et al , 2008Williams et al 2013a;Kapranas et al 2017). The LPW is the most important pest of tree seedlings in replanted coniferous forests in Northern Europe (Evans et al 2015).…”

“…EPNs are the most promising biological control agents of LPW applied in augmentative fashion (Torr et al 2005;Brixey et al 2006;Dillon et al 2006Dillon et al , 2007Dillon et al , 2008Williams et al 2013a, b;Kapranas et al 2017). It has been shown that EPN species with different foraging strategies give adequate control in particular with reference to accepted infestation thresholds of 20 weevils per stumps, in a variety of forest soils, including both peats and mineral soils (Wainhouse et al 2007;Kapranas et al 2017;unpublished note Coillte, Ireland).…”

The impact of entomopathogenic nematodes on a non-target, service-providing longhorn beetle is limited by targeted application when controlling forestry pest Hylobius abietis

“…To kill immature stages of the large pine weevil, 3.5 million IJs are applied in a water suspension around coniferous tree stumps (Brixey et al, 2006;Dillon et al, 2006Dillon et al, , 2007, which constitute the pest microhabitat (Leather et al, 1999). For weevil suppression on an operational level (i.e.…”

“…Dillon, personal communication). Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae), which is commercially produced and exotic to Ireland (Hominick, 2002), is the main EPN species currently in use against H. abietis, though Heterorhabditis downesi Stock, Burnell and Griffin (Nematoda: Heterorhabditidae), a native Irish species (Griffin et al, 1991), has been evaluated for use against H. abietis in pilot trials (Dillon et al, 2006(Dillon et al, , 2007Skrzecz and Majewski, 2010). While EPN present a promising alternative to chemical control methods and may play an important role in achieving sustainable forest management, their ability to infect and reproduce in a wide range of insects also presents a risk to non-target insects in the targeted habitat (Bathon, 1996;van Lenteren et al, 2003).…”